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Date:   Sat, 1 Apr 2023 01:09:18 -0300
From:   Wedson Almeida Filho <wedsonaf@gmail.com>
To:     Gary Guo <gary@garyguo.net>
Cc:     rust-for-linux@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        linux-kernel@vger.kernel.org,
        Wedson Almeida Filho <walmeida@microsoft.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 10/13] rust: introduce `Task::current`
Message-ID: <ZCeubhgETf84thv9@wedsonaf-dev>
References: <20230330043954.562237-1-wedsonaf@gmail.com>
 <20230330043954.562237-10-wedsonaf@gmail.com>
 <20230331034701.0657d5f2.gary@garyguo.net>
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Gary, thanks for reviewing!

On Fri, Mar 31, 2023 at 03:47:01AM +0100, Gary Guo wrote:
> 
> I don't think this API is sound, as you can do `&*Task::current()` and
> get a `&'static Task`, which is very problematic.

One thing that isn't clear to me is: how do you get a 'static lifetime in the
example above?

Altough `TaskRef` does have an arbitrary lifetime param, that's not the lifetime
that the returned `Task` reference gets. For illustration, I've explicitly added
a lifetime 'a in the impl below:

impl Deref for TaskRef<'_> {
    type Target = Task;
    fn deref(&'a self) -> &'a Self::Target {
        self.task
    }
}

Which means that the borrow of the `TaskRef` you use to call `deref` must
outlive the returned `Task`.

So how do you get a `TaskRef` with a static lifetime to begin with? Or is there
another trick to get the `&'static Task` that I can't see?

Thanks,
-Wedson